Project Summary: The decline of cortical plasticity due to closure of the juvenile-specific critical period is the key impedance of recovery from neurodevelopmental disorders and brain trauma in later life. Neuromodulatory systems are abundant in the adult cortex and well-positioned to orchestrate experience-dependent physiological events to prompt robust plasticity. However, an increasingly recognized complexity of neuromodulatory circuits as well as the diversity of neuron subtypes pose a challenge to identify a specific neuromodulatory system and their cortical target to precisely restore plasticity. The goal of this study is to identify novel molecular and circuit targets for inducing neuromodulatory changes in the adult brain, to reactivate juvenile-like plasticity for treating brain disorders with enduring functional impairments. Using ocular dominance plasticity, a prevailing primary visual cortex critical period plasticity model, We will test the hypothesis that, among various possible combinations of neuromodulatory systems, and their cortical targets, nicotinic ACh modulation and somatostatin expressing interneurons in the deep layer of primary visual cortex expressing specific type of nicotinic ACh sub-type as a novel combination of neurmodulatory circuit elements to induce rapid local circuit modulation to restore juvenile-like visual cortex plasticity and recovery from Amblyopia in adulthood. We will test this hypothesis by taking full advantage of the recently developed genetically-engineered mouse lines to achieve sub-population and cortical-layer-specific circuit-selective manipulation and measurement of gene expression or neural activity beyond conventional cell-type level analysis in combination of in vivo extracellular and in vitro slice electrophysiology with optogenetics, chemogenetics, and behavior assay. In Aim1, we will examine the contribution of specific nAChR subunit?on inducing experience-dependent rapid change of deep layer interneurons to trigger ocular dominance plasticity. In Aim2, we will dissect the excitatory and inhibitory circuit mechanisms regulated by deep layer SST interneurons to trigger ocular dominance plasticity. In Aim3, we will examine the extent of recovery from Amblyopia by modulating nAChR in deep layer interneurons. Successful completion of this project will illuminate new molecular and circuit mechanisms that gate the initial cascade triggering cortical plasticity, which will have direct implications for Amblyopia, a condition with limited adult-applicable treatment affecting 2?5% of the human population, but also for brain injury repair, sensory recovery, and the treatment of neurodevelopmental disorders with sensory perceptual deficits.